1. Field of the Invention
The present invention relates to an optical storage device, and in particular to an optical storage device and method for accurate compensation of a speed error signal.
2. Description of the Related Art
FIG. 1 is a schematic diagram showing the architecture of a conventional speed control of an optical storage device according to the prior art. A predetermined speed signal is provided as a voltage signal. A comparison device 14 compares the predetermined speed signal and a feedback speed signal to generate a speed error signal, output to a microprocessor 17. The microprocessor 17 calculates the speed error signal, and then output a calculated result to a feedback controller 19. The feedback controller 19 generates a tracking control effort signal, output to an optical head module 12. The optical head module 12 is operated at an actual speed according to the tracking control effort signal. A measurement device 13 detects the actual speed and generates an actual speed signal. A gain controller 24 increases the actual speed signal to generate the feedback speed signal.
General speaking, a speed error signal comprises a DC steady state error (ess). In conventional speed control method, the DC steady state error can be easily eliminated by the microprocessor 17, because the DC steady state error always has the same value (ess+=ess−) in a horizontal orientation no matter the optical head module 12 increases or decreases the moving speed, wherein + indicates increased moving speed, and − indicates decreased moving speed, thereby the optical head module 12 is controlled effectively when in the horizontal orientation.
Moving inertia is affected in a non-horizontal orientation (for example, vertical orientation) when the optical head module 12 moves. For example, the moving speed is affected by gravitational force when the optical head module moves in different directions. As a result of gravitational force, the microprocessor 17 can not eliminate the DC steady state error because of the different DC steady state errors (ess+≠ess−) when the optical head module increases or decreases its moving speed. Thus, the feedback controller 19 generates the different tracking control efforts when the optical module increases and decreases its moving speed and the different tracking control efforts will lead to a tracking failure.
Moreover, as the demands of vertical type optical disk drive have increased, moving speed is affected by gravitation force, such that the optical head module 12 cannot shift precisely to a target track when the DC steady state error in the speed error signal is abnormal (ess+ or ess−), thereby the optical storage device is made to be further unstable and creating many potential problems, including increased seek time.